Ore preparation



United States Patent O "ice vama No Drawing. Original Nu. 2,111,829,.1ktgd September 13,1955, Serial No. 190,669, October 17,,19s0. ,Ap 1rcatloir for reissue'March 14, 1957, Serial No. 646,184

Matter enclosed in liea'vy brackets]: 1 appears in the original patent but forms no part of'this" reissue specifi-' canon; matter printed" in italics indicates the additions made byreissue'.

I This invention relates to the separation of metal values from iron ores; and more particularly to the separation of small quantifies of nickel and/or cobalt from iron ore of the nickeliferouslateritic, or Mayari, type.

The principal object of this invention is to effect a satisfactory separation: of nickel and/or cobalt fromroasted iron ores, when such ores are leached" with ammonium' carbonate solution.

Another object is to recover ammonium carbonate leaching solution forre-use.

A further object is to obtain-nickel and/or cobalt compounds in a form. readily'separated from solution.-

Still another object is to recover iron ina form readily separated from aqueous" nickel salt solutions.

It has long been. known to leach ores with ammonium carbonate to separate metal values, such as nickel and cobalt, from other metal constituents; by treating under atmospheric conditions of temperature and pressure. The leaching method hasbeentusedxwith nickel ores to separate nickel from small amounts of iron, and likewise with iron ores to separate iron from small amounts of nickel, as well as cobalt if present. When it is desired to separate iron, presentin iron oreasferric oxide, from small amounts of nickel or'cobalt by means of an ammonium carbonate leach; a reducing roast must pre cede the leaching step. During. roasting, nickel and/or cobalt are reduced to the elemental metaland great care must be used to halt the'rednction just short of the'point at which'metallic iron. is formed; When the: ore is"- over reduced, i. e., w hen considerable metallic iron is present prior to leaching, considerable diificulty is encountered in separating the nickel from the precipitated iron com.- pouncls, possibly because of the large amount of gela tinous ferric hydroxide present. In refining a nickelcontaining iron ore for. use in: the blast furnace, for'example, it is mandatory that nickel be almost entirely removed from the ore. While, as has been pointed out, nickel may be satisfactorily removed from the: me by prior ammonium carbonate leaching methods; the close control required in roasting the ore previous to the leaching step involves a tedious procedure.

I have found that by reducing an arc of the nickeliferous' late'ritic type, which may or may not contain cobalt, to the point at which nickel and/or cobalt are reduced to the metallic state, satisfactory separation or without regard to the extent of reduction of the iron if the iron from the nickeliferous' metal values is obtained the subsequent leach: with ammonium carbonate is made at elevated pressure and temperature, and in the presence of ammonia gas. I have found my process to: give excellent results when treating an. ore of the Mayari type.- found' in Cuba, in which nickel may bepresent'in quantitles of from 0.05 l .7 5%, and cobalt if present range from 0.050.20%. Moreover, over-reduction of Re. R'eiat d OeaS, 1957 the ore does not have a deleterious efiect on the sep# aration by my process, separation having been made wherein up to 78% of the iron in the ore has been reduced to the metallic state. For purposes of this invention, when speaking of nickeliferous iron ore, I mean to include those iron ores which contain nickel, as well as those which contain both nickel and cobalt. The term nickel values as used herein applies to nickel, or nickel and cobalt, for cobalt, when present, isbelievedto'actin the same manner as nickel. The reducing roast is performed in order to convert tlie'nickeiandcobalt coinpounds, present presumably as silicates or oxides, toy-a" state in which they are amenable to the ammonium calbonate leaching treatment. when, after such a roast, nickel and cobalt are treated with ammonium carbonate solution, nickel ammonium carbonate complex'and cobalt ammonium carbonate complex are formed. These complexes are soluble in an aqueous solution of ammonium carbonate under atmospheric conditions of temperature and pressure, and-can thus be separated from the solid iron compounds. By my invention I can take a nickeliferous iron ore, which has been reduced to any state varying between that at which the nickeliferous values are just completely reduced to metal, while little or none of the iron has been reduced to metal, up to a state of substantial-ly complete reduction of the ore, which for practical purposes may be said to be" that point at which about 78-80% of the iron has been reduced to' metallic iron, and leach saicl reduced ore with ammonium carbonate' at elevated temperature and pressure by meansof an autoclave and obtain satisfactory separation of iron from nickelife rous material.

While prior methods of leaching required, for satisfactory separation, a reduced ore having very little metallic iron, or one in which the ironwaspresent as magnetite plus some wiisti'te', by my autoclaving' treatment- I not only can treatsatisfactorily ore thus reduced, but

also can obtain satisfactory separation of metal values- With olre that has been reduced to any degree beyond that point, including the state at which most of'the" iron is in the form of sponge. My method eliminates the neces sity for close time and temperature control overthe reducing step, thus permitting a wider variety of reducihg conditions, with a consequent decrease intime for the actual reducing operation.

Another feature of my invention resides in the recovery of ammonium carbonate leach solution.

tion, containing regenerated ammonium hydroxide and ammonium carbonate, can again be used for the. leachingof a fresh batch of reduced ore.

One example of effecting: separation. of nickel values from the iron ore' by use of high temperature and pressu're is given below, and is" illustrative of my process:

An iron ore containing 1.48%. nickel and greater than 0.10% cobalt, was reduced with pure hydrogen at approximately 1400 F., so that any nickel andv cobaltcompounds present were reduced to the metallic state. During the reducing step, iron, originally presentin the ore as ferric oxide, was also reduced; I l

Depending on the degree of reduction, as has been explained, iron may now be present in reduced state I have; found that while nickel ammonium carbonate complex in one of several forms. The simplest reduction would produce iron essentially as ferrous-ferric oxide (magnetite) and possibly containing some wiistite. A more severe reduction would result in some magnetite, wiistite, and some metallic iron being formed. 1 In this particular case, metallic iron, after reduction, was in excess of 75% of the total iron. The reduced ore Was mixed with ammonium carbonate leach solution to form a slurry, and was then ready for the autoclaveleach treatment. The slurry, along with more leach solution, said solution containing approximately 18% ammonium carbonate, 0.02% sodium cyanide and 9% ammonia (NHs) dissolved therein, was introduced into an autoclave and autoclave-leached at 300 F. for two hours. Prior .to heating the autoclave, ammonia gas and oxygen were bled into the closed system, raising the total pressure to 200 p. s. i. As the autoclave tempera ture was raised to an ultimate of 300 F., the total pressure increased to 650 p. s. i. at the maintained temperature. During the leaching process .the metallic nickel reacted with ammonium carbonate to form nickel ammonium carbonate complex which remained in solution at the particular temperature and pressures used. After autoclaving, the slurry was removed to a thickener. The hydrated iron compounds formed during the autoclaveleach, took the form of a partially hydrated ferric oxide which had rapid filtering and settling characteristics.

This latter fact aids in separating iron from the nickel insolution during the filtration step which follows the thickener operation, and 'gives an important advantage over atmospheric leaching.

J The pressures and temperatures employed during this autoclaving operation may vary considerably but they must be such as hold the nickel in solution. Preferably, the pressure should be at least 175 lbs. per square inch, and the temperature should be at least 250 F.

, The residue recovered by filtration was washed, first with ammonium carbonate solution and then with water. At this point the primary purpose of the invention has been accomplished, that of separating nickel values from the iron so that any nickel values remaining in the iron are of such low order of magnitude that the iron oxide may be used successfully in the manufacture of pig iron. The iron oxide residue from one sample of ore, treated by the process given in the foregoing description, analyzed as follows:

The above analysisshows that nickel and cobalt were eliminated from the ore to a point where they are no longer a problem in iron smelting operations.

Chromium and aluminum can be separated from the iron by well known methods.

While the nickel values, in the above example, were soluble in the aqueous solution during the autoclaving step at 300 F., and at the pressure given, and remained so upon cooling the slurry after autoclaving, which fact enabled me to separate the solution from the iron residue by filtration, I was able, by reintroducing the filtrate to an autocalve, and heating for two hours at a temperature just above 400 F., with consequent increase of pressure, but in the absence of added ammonia gas, to precipitate the nickel values, possibly as nickel carbonate, and thus recover them from the leach solution by a further filtration step. The filtrate from this second filtering operation contained substantially pure ammonium carbonate leach solution which can be returned to the original autoclave leach operation.

Thus, by using two autoclaves, one for leaching and the other for recovering nickel values, I am able to maintain a closed circuit whereby there is little or no loss in ammonium carbonate leaching solution.

Apparently the solubility of nickel in the ammonium carbonate solutions under pressure is related to the partial pressure of ammonia gas. When suflicient ammonia gas is introduced into the autoclave at the outset, the temperature canbe raised to 300 F., or 400 F., and nickel will remain in solution. However, when, as mentioned above, no ammonia gas is introduced into the autoclave, nickel will be precipitated when the temperature is raised to 400 F.

In the practice described above, most of .the nickel is dissolved during the autoclaving operation, as the mixture of ore and reagent go directly intov the autoclave. This is my preferred practice. However, theprocessumay be modified by; first making the slurry' of ore and reagent and permitting a portion of the nickel to be dissolved at atmospheric pressures and then autoclaving the mixture. It is essential in both the preferred practice and in the modification just described that the autoclaving operation be performed, upon the mixtures of ore, reagent and solution, as the autoclaving at high temperatures and pressures not only increases the amountof nickel dissolved from the ore but facilitates the removal of solution from the insoluble portion of the ore following the autoclaving treatment.

While the figures given in the herein described examples for time, temperature and pressure are eminently satisfactory for the particular cases described, it should be explained that my invention can be performed under a wide range of operating conditions. Due to the fact that alteration of any one of the following conditions, viz., time, temperature, pressure, concentration of solution, amount of recirculation, and partial pressure of ammonia gas and oxygen gas, may affect the conditions of time, temperature and/or pressure required to maintain nickel values in solution during autoclaving, it is evident that the range of operating characteristics necessary for each and every given condition must remain empirical in na: ture. While the many variables which may be introduced during the autoclave-leach operation necessitate an indefiniteness as to maximum and minimum operating conditions to meet all situations, such indefiniteness of extreme conditions in no way detracts from the fundamental concept and advance in the art provided by my invention. It is likewise true, when autoclaving a nickel carbonate solution to precipitate nickel salt, that the optimum conditions for time, temperature and pressure may vary as the concentration of the solution varies.

I claim:

1. A method of treating a ferrous ore containing nickel in excess of 0.25 percent to remove nickel therefrom, which comprises reducing said ore to a point at which substantially all of the nickel has been reduced to elemental metal, then treating said ore in the presence of an aqueous ammonium carbonate solution, a free-oxygencontaining gas and ammonia gas at a pressure of at least pounds per square inch and at a temperature of at least 250 F.

2. A method of treating a ferrous ore containing nickel in excess of 0.25 percent to remove nickel therefrom, which comprises reducing said ore to. a point at which substantially all of the nickel has been reduced to elemental metal, forming a slurry with said ore and treating said slurry in the presence of ammonium carbonate, a free-oxygemcontaining gas and ammonia gas at a temperature at least 250 F. and at a pressure of at least 175 pounds per square inch for at least 30 minutes.

3. A method of treating a ferrous ore containing nickel in excess of 0.25 percent to remove nickel therefrom,

which comprises reducing said ore to a point at which substantially all of the nickel has been reduced to elemental metal, forming a slurry with said ore and treating said slurry in the presence of an aqueous ammonium carbonate solution, a free-oxygen-containing gas and ammonia gas at a pressure of at least 175 lbs. per square inch and at a temperature of at least 250 F. and thereby forming a nickel bearing solution, separating the nickel bearing solution from said treated slurry and heating the solution at higher pressures and temperatures than in the previous treatment and in the absence of added ammonia gas to separate nickel compounds from said solution.

4. A method of treating a ferrous ore containing nickel in excess of 0.25 percent to remove nickel therefrom, which comprises reducing said ore to a point at which substantially all of the nickel and at least some of the iron has been reduced to elemental metal, forming a slurry with said ore and treating said slurry in the References Cited in the file of this patent or the original patent UNITED STATES PATENTS 2,531,336 Hills et a1 Nov. 21, 1950 

